The present disclosure relates to combustion engines and in particular to a method of cleaning an exhaust gas recirculation valve (EGR valve) of an engine system.
It is well known to provide a combustion engine with an exhaust gas recirculation system in which exhaust gas is recirculated back from an exhaust side of the engine to an air inlet side of the engine.
Such exhaust gas recirculation systems include a valve referred to as an EGR valve to control the flow of exhaust gas flowing back to the inlet side of the engine.
Such EGR valves normally have a poppet type valve having a valve element comprised of a valve head and valve stem with the valve head being connected to a valve actuator via the valve stem and the valve head co-operating with a valve seat when in a closed position.
Current EGR systems operate at low ambient temperatures, but not when the engine is very cold due to the risk of fouling and sticking of the EGR valve. Using current practice the main contamination that builds up on the EGR valve is a mix of dry soot produced at exhaust gas temperatures of circa 150 to 250° C. and lacquer produced at exhaust gas temperatures of circa 80 to 150° C. Current practice to clean the EGR valve is to cycle the EGR valve repeatedly through its range of movement from fully open to fully closed and back. This action “scrapes” any deposit accumulation on the valve stem.
However, because opening the EGR valve fully causes a very high rate of EGR to flow if used during normal engine running, the cleaning cycle is only be performed with the engine off, typically at the end of a drive cycle.
Forthcoming exhaust emission regulations particularly for diesel engines will require the operation of EGR systems at conditions where they have not previously been used and, in particular, at low ambient temperatures with cold engine coolant, that is to say, during an engine warm-up period following a cold start when the exhaust gas temperature is below 80° C.
Opening the EGR valve in such cold conditions when the exhaust gas and the EGR valve are both relatively cold will cause sticky hydrocarbons to condense out of the exhaust gas and accumulate on the valve. Such fouling of the EGR valve is undesirable as it will often cause unreliable operation of the EGR valve such as valve sticking in which the EGR valve will get stuck in a partially open condition when the desired operational position is closed or will get stuck open when a closed position is required.
Such valve sticking will result in a reduction in emission performance and potential poor engine running.
The current cleaning procedure that is effective for removing lacquer and dry soot generated during current EGR operating regimes will no longer be adequate to remove the sticky residue that is produced when using EGR operation in such cold conditions and a new cleaning process is required.
It is an object of the present disclosure to provide a method of cleaning an EGR valve that is able to effectively remove the sticky residue produced by cold EGR operation before the build-up of such residue adversely affects EGR valve operation.
According to a first aspect of the present disclosure there is provided a method of cleaning an exhaust gas recirculation valve forming part of an engine system having an engine arranged to supply exhaust gas to a particulate filter, an exhaust gas recirculation circuit including the exhaust gas recirculation valve to selectively recirculate exhaust gas back from an exhaust side of the engine to an air inlet side of the engine, and an electronic controller to control the operation of the engine system, wherein the method comprises producing an estimate of accumulated combustion by-product fouling of the exhaust gas recirculation valve, comparing the estimate of combustion by-product fouling to a predefined fouling limit and, if the estimate of combustion by-product fouling is greater than the predefined fouling limit, operating the engine to increase a temperature of the exhaust gas from the engine while producing a flow of exhaust gas having a an unburnt hydrocarbon content below a threshold, and controlling the exhaust gas recirculation valve during a cleaning period to allow the exhaust gas from the engine to flow through the exhaust gas recirculation valve thereby reducing a quantity of combustion by-products accumulated at the exhaust gas recirculation valve.
This has the advantage that sticky hydrocarbon residue and other fouling of the EGR valve are burnt-off.
There may be lower and upper predefined fouling limits and the lower limit may be a fouling limit above which cleaning of the exhaust gas recirculation valve is used to reduce the probability of unreliable operation of the exhaust gas recirculation valve. Accordingly, the method may further comprise, responsive to the estimate of combustion by-product fouling exceeding the lower limit, adjusting operation of the engine system to clean the exhaust gas recirculation valve in order to reduce the probability of unreliable operation of the exhaust gas recirculation valve.
If the estimate of combustion by-product fouling is greater than the upper fouling limit then the engine may be immediately operated to increase the temperature of the exhaust gas from the engine while producing a flow of hot exhaust gas having a low unburnt hydrocarbon content and the exhaust gas recirculation valve may be controlled to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve. Accordingly, the method may further comprise operating the engine system in a first mode in which the estimate of combustion by-product fouling is greater than the upper limit, and during operation in the first mode, adjusting operation of the engine system to increase the temperature of the exhaust gas from the engine and produce a flow of exhaust gas having an unburnt hydrocarbon content below the threshold, and at least partially opening the exhaust gas recirculation valve to allow exhaust gas from the engine to flow through the exhaust gas recirculation valve.
If the estimate of combustion by-product fouling is greater than the lower fouling limit but lower than the higher fouling limit then operation of the engine to increase the temperature of the exhaust gas from the engine while producing a flow of hot exhaust gas having a low unburnt hydrocarbon content may be delayed until a particulate filter regeneration event commences and when the particulate filter regeneration event commences the exhaust gas recirculation valve may be controlled to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve. Accordingly, the method may further comprise operating the engine system in a second mode in which the estimate of combustion by-product fouling is greater than the lower limit but less than the upper limit, and during operation in the second mode, waiting until a particulate filter regeneration event commences, and then adjusting operation of the engine system to increase the temperature of the exhaust gas from the engine while producing a flow of exhaust gas having an unburnt hydrocarbon content lower than the threshold, and controlling the exhaust gas recirculation valve to allow the exhaust gas from the engine to flow through the exhaust gas recirculation valve.
This has the advantage that no additional fuel is required to clean the EGR valve.
The exhaust gas recirculation valve may be closed if one of the flow of hot exhaust gas having a low unburnt hydrocarbon content ceases, an updated estimate of the accumulated combustion by-product fouling of the exhaust gas recirculation valve indicates that the level of fouling is below a predefined fouling threshold and an EGR valve maximum permitted temperature threshold is reached.
The predefined fouling threshold may be a level of fouling at which the quantity of combustion by-products accumulated at the exhaust gas recirculation valve is substantially equal to zero.
The estimate of accumulated combustion by-product fouling of the exhaust gas recirculation valve may be an integral of a rate of fouling of the exhaust gas recirculation valve over time.
The rate of fouling of the exhaust gas recirculation valve may be based upon a combination of a relationship between exhaust gas mass flow through the exhaust gas recirculation valve and temperature of the exhaust gas flowing through the exhaust gas recirculation valve and a relationship between ambient air temperature and engine coolant temperature during the time period that exhaust gas is flowing through the exhaust gas recirculation valve.
The relationship between exhaust gas mass flow through the exhaust gas recirculation time and temperature of the exhaust gas flowing through the exhaust gas recirculation valve may be provided by way of a look up table and the relationship between ambient air temperature and engine coolant temperature during the time period that exhaust gas is flowing through the exhaust gas recirculation valve may be provided by way of a look up table.
Controlling the exhaust gas recirculation valve during a cleaning period may comprise producing an exhaust gas recirculation valve position based upon a relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the cleaning period and a pressure difference across the exhaust gas recirculation valve.
The relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the cleaning period and a pressure difference across the exhaust gas recirculation valve may be provided by way of a look up table.
The exhaust gas mass flow through the exhaust gas recirculation valve during the cleaning period may be based upon a combination of a relationship between the temperature of the exhaust gas flowing through the exhaust gas recirculation valve and engine coolant temperature and a relationship between time and exhaust gas recirculation valve temperature during the cleaning period.
The relationship between the temperature of the exhaust gas flowing through the exhaust gas recirculation valve and engine coolant temperature may be provided by way of a look up table.
The relationship between time and exhaust gas recirculation valve temperature during the cleaning period may be provided by way of a look up table.
The engine may be a diesel engine and the particulate filter may be a diesel particulate filter.
According to a second aspect of the present disclosure there is provided an engine system comprising an engine arranged to supply exhaust gas to a particulate filter, an exhaust gas recirculation circuit including an exhaust gas recirculation valve to selectively recirculate exhaust gas from an exhaust outlet side of the engine to an air inlet side of the engine and an electronic controller to control the operation of the engine and the exhaust gas recirculation valve wherein the electronic controller includes instructions stored in non-transitory memory which are executable by a processor to produce an estimate of accumulated combustion by-product fouling of the exhaust gas recirculation valve based upon inputs received from a number of sensors, compare the estimated combustion by-product fouling to a predefined fouling limit stored in the non-transitory memory of the electronic controller and if the comparison indicates that the estimate of combustion by-product fouling is greater than the predefined limit the electronic controller is arranged to clean the exhaust gas recirculation valve by operating the engine to increase the temperature of the exhaust gas from the engine while producing a flow of exhaust gas having a low unburnt hydrocarbon content and to control the exhaust gas recirculation valve during a cleaning period to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve thereby reducing the quantity of combustion by-products accumulated at the exhaust gas recirculation valve.
There may be lower and upper predefined fouling limits and the lower limit may be a fouling limit above which cleaning of the exhaust gas recirculation valve is used in order to reduce the probability of unreliable operation of the exhaust gas recirculation valve.
If the estimate of combustion by-product fouling is greater than the upper fouling limit then the electronic controller may be arranged to operate the engine to immediately increase the temperature of the exhaust gas from the engine while producing a flow of hot exhaust gas having a low unburnt hydrocarbon content and is further arranged to control the exhaust gas recirculation valve to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve. For example, the electronic controller may further comprise instructions stored in the non-transitory memory and executable by the processor to operate the engine system in a first mode in which the estimate of combustion by-product fouling is greater than the upper limit, and during operation in the first mode, adjust operation of the engine system to then the electronic controller is arranged to operate the engine to immediately increase the temperature of the exhaust gas from the engine and produce a flow of exhaust gas having an unburnt hydrocarbon content below the threshold, and control the exhaust gas recirculation valve to allow exhaust gas from the engine to flow through the exhaust gas recirculation valve.
If the estimate of combustion by-product fouling is greater than the lower fouling limit but lower than the upper fouling limit then the electronic controller may be arranged to delay operating the engine to increase the temperature of the exhaust gas from the engine while producing a flow of hot exhaust gas having a low unburnt hydrocarbon content until a particulate filter regeneration event commences and when the particulate filter regeneration event commences the electronic controller is arranged to open the exhaust gas recirculation valve to allow hot exhaust gas from the engine to flow through the exhaust gas recirculation valve. For example, the electronic controller may further comprises instructions stored in the non-transitory memory and executable by the processor to operate the engine system in a second mode in which the estimate of combustion by-product fouling is greater than the lower limit but lower than the upper limit, and during operation in the second mode, wait until a particulate filter regeneration event commences, and then adjust operation of the engine system to increase the temperature of the exhaust gas from the engine while producing a flow of exhaust gas having an unburnt hydrocarbon content lower than the threshold, until a particulate filter regeneration event commences, and when the particulate filter regeneration event commences, at least partially open the exhaust gas recirculation valve to allow exhaust gas from the engine to flow through the exhaust gas recirculation valve.
The exhaust gas recirculation valve may be closed if one of the flow of hot exhaust gas having a low unburnt hydrocarbon content ceases, an updated estimate of the accumulated combustion by-product fouling of the exhaust gas recirculation valve indicates that the level of fouling is below a predefined fouling threshold and an EGR valve maximum permitted temperature threshold is reached.
The predefined threshold may be a level of fouling substantially equal to zero.
The estimate of accumulated combustion by-product fouling of the exhaust gas recirculation valve may be an integral of a rate of fouling of the exhaust gas recirculation valve over time.
Controlling the exhaust gas recirculation valve during a cleaning period may comprise producing an exhaust gas recirculation valve position based upon a relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the cleaning period and a pressure difference across the exhaust gas recirculation valve.
The relationship between exhaust gas mass flow through the exhaust gas recirculation valve during the cleaning period and a pressure difference across the exhaust gas recirculation valve may be provided by way of a look up table stored in a memory of the electronic controller.
The engine may be a diesel engine and the particulate filter may be a diesel particulate filter.
According to a third aspect of the present disclosure there is provided a motor vehicle having an engine system wherein the engine system is an engine system constructed in accordance with said second aspect of the present disclosure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.